A great resource to understanding everything about manure are the Tri-Provincial Manure Application and Use Guidelines.(2)

Nutrient management is particularly important in Manitoba due to the large expansion of the hog industry over the last few decades. Although manure is an ebxcellent source for plant nutrients, the expansion to more than 8 million hogs in 2010 has resulted in the challenge of too much manure and not enough land-base for spreading.(3) The large amount of manure created and the resulting nitrous oxide (N2O) should make manure management a priority when trying to reduce greenhouse gas (GHG) emissions from farms. Approximately 9 percent of Manitoba’s agricultural GHG emissions are created due to manure storage and management.(4)

Major emissions from manure come in the form of methane (CH4) from anaerobic decomposition of manure during storage, and N2O formed during storage and application.

The creation of these gases is influenced by a variety of factors: temperature, oxygen level, moisture or amount of nutrients.

In turn, these factors are affected bymanure type, animal diet, the type of manure storage and handling, and manure application techniques.(5) To help reduce GHG creation and work with large amounts of excess manure, it is important that manure management in the province concentrates on disposing manure in an environmentally and economically friendly manner.

Objectives for manure management should focus on maintaining or improving local water and air quality by limiting unpleasant odors, reducing nitrogen (N) and phosphorus (P) concentrations in manure and efficiently spreading manure. Although many management technologies exist, not all are realistic or cheap enough for farmers to implement. Different nutrient management strategies will work better for different farms.

Manure handling systems

Emissions from manure handling systems are released when favourable conditions are met for gas creation. Warm, wet conditions tend to create higher amounts of both CH4 and N2O.

To reduce gaseous emissions when handling manure ensure that manure is not left in the barn environment for extended periods of time. Manure kept in a barn will tend to be warmer than manure stored outdoors and will produce more methane. Keeping barns clean and dry will help lower the loss of ammonia, reducing N2O production.(6) Barn scraper systems can provide regular manure removal from the barn and store waste in proper storage areas.

Solid manure management systems, where poultry and livestock are housed on dry bedded manure packs of straw or sawdust were found to have lower CH4 emissions when compared to liquid or slurry handling systems.(7)

Manure storage systems

Manure storage is one of the main areas where a farmer can control how many nutrients remain in or are lost from the manure. It is in the best interest of the farmer to focus on what method of storage system is best for the farm and type of livestock. Certain manure storage systems are more environmentally friendly than others, but may not be the best fit for the type of livestock the farmer is raising.

The following practices are encouraged:

Avoid liquid or slurry handling systems – Methane production takes place when manure decomposes in the absence of oxygen (anaerobic conditions). Therefore, CH4 production is higher in liquid manure.(8)

Use manure storage covers – roofs for solid, covered tanks for liquid – to trap manure gases. In liquid systems, covers may reduce methane emissions by up to 95 percent.(9) Covers also have the added benefit of controlling odour. Odour means that gas and money is being lost!!

Eliminate winter spreading

Winter manure application should be eliminated to prevent manure runoff at spring-thaw and to reduce spring-thaw N2O emissions.

Effective November 10, 2013, the spreading of livestock manure between November 10 and April 10 in Manitoba is prohibited under The Environment Act: Livestock Manure and Mortalities Management Regulation, unless otherwise noted.(17)

Applying manure after April 10 encourages farmers to apply manure at a time when their crops are just beginning to grow. The developing crop uses the nutrients as they become plant-available, minimizing the risk of loss to the environment.(18)

Should moving manure during the winter be necessary, it is recommended that the manure be stock-piled in the field and spread following spring-melt.

Composting manure

Composting breaks manure into a more stable organic form, slowly releasing nutrients over time. Compost is rich in C, free from most pathogens and weed seeds, and improves soil nutrient status. Because compost reduces the amount of synthetic fertilizer needed on fields, composting manure helps lower net GHG emissions from livestock systems. The aerobic (with air) method of decomposing manure is also thought to lower CH4 and N2O creation.(19) However, more research is needed to determine the exact benefit of composting manure net GHG reduction.

Consider anaerobic digesters

Anaerobic digestion is the oxygen-free process through which manure is broken down by microbes. The microbes produce a mix of CH4 and CO2, called biogas. This biogas can be cleaned and used as a natural gas replacement, burned as fuel or used by a generator to produce electricity or heat.(20) The remaining organic material left after the digestion process has some nutritional value, very little odor and can be applied to fields as fertilizer.

Current anaerobic digesters on the market are much too expensive for most farmers to own. Research continues at the University of Manitoba to determine the benefits of digesters on manure management.(21)

This digestion system works better for dairy and cattle manure, as poultry and swine manure presents more of a challenge due to their higher nitrogen levels.(22) Anaerobic digestion is known to reduce pathogens, odour and weed seeds in the digested manure, reduce GHG emissions and provides an alternative fuel source.(23)

Digesters may be the technology of the future to lower farm fuel consumption or provide alternative energy creation.